Overview of materials for Gray Cast Iron

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Posted by Penticton Foundry

ASTM A48 Class 30 (Related Standards – DIN GG20, BS 1452 Grade 220) is a gray cast iron. Gray iron consists of graphite flakes in a metallic matrix. When fractured, it is grayish in colour – hence the name (specifically, a fracture will follow along the graphite flakes which are gray).  The low cost of production and attractive properties make gray iron one of the most commonly used ferrous alloys.  Gray iron class 30 is one grade in a family of many.  Chemistry ranges are not specified in the ASTM A48 standard. Instead, chemistry and hardness values listed in this data sheet would be typical for a class 30. 

Read: If you’re interested in comparing gray iron and ductile iron read “Ductile Iron Versus Gray Iron Castings.”

Composition

C

Mn

Si

P

S

Min%

3.1

0.5

2.1

.02

.05

Max%

3.3

0.9

2.3

0.1

0.12

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Physical and Mechanical Properties

UTS (ultimate tensile strength)

30,000 psi (207MPa)

Hardness

174 – 210 BHN

Density lb/in3 (g/cm3)

0.258 (7.15)

Thermal Conductivity   Btu/hr·ft·F (W/m·K)

30 (53) at 212°F (100°C).  Will drop as temperature increases.

Specific Heat at 70F  Btu/lb·F (J/Kg·k)

0.14 (586)

Coefficient of Thermal Expansion Ɛ/F(Ɛ/C)X106 average between 68-212F

5.8 (10.5)

Melting Temperature

2050 – 2120 F

Compressive Strength Ksi (MPa)

109 (752)

Gray Iron Properties and Advantages

• Gray iron has great vibration and sound damping properties.  For this reason, it is still one of the best materials for machine bases
• Great thermal conductivity because of its network of graphite flakes
• Good strength in compression – typically 3-4 times that of its ultimate tensile strength
• Excellent machinability due to the presence of the graphite flakes 
• Fluidity during pouring means that it can be cast into thin sections and complex shapes

Applications

• Automotive (brake drums, clutch plates, heads, cylinder liners, pistons)
• Ingot moulds
• Machine-tool parts
• Heavy duty diesel engine blocks
• Gearboxes
• Flywheels
• Counterweights
• Municipal-street castings
• Pipe
• Valves
• Pumps (and pump parts)

Read: To learn more about gray iron, please check out our gray iron webpage.

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